The objective of the NIMH Psychoactive Drug Screening Program (PDSP) is to provide broad screening capabilities (pharmacological and functional assays) and receptor binding data to the scientific research community to stimulate innovative research and development efforts in the discovery and design of novel psychoactive compounds for basic research, neuroimaging, and as potential therapeutic agents in the treatment of psychiatric disorders. Activities of the PDSP include screening currently used pharmacological tools and therapeutics to profile their activity, screening compounds with functional or behavioral effects to identify their receptor targets, selectivity screening of new potential research tools and imaging ligands, in vitro efficacy testing and counter-screening of potential therapeutics, and screens of synthetic and natural product libraries with unknown activity. In addition, the program supports a large database of affinity constants for thousands of compounds at hundreds of receptors. This data can be mined to provide starting points for new tool or drug discovery projects or identify potential new targets for intervention. Currently, the program has over 225 assays available for screening, including in vitro ADME and toxicity screens.